The present invention is directed to flying spot scanners (commonly referred to as raster output scanners (ROSs)) which typically have a reflective multifaceted polygon mirror that is rotated about its central axis to repeatedly sweep one or more intensity modulated beams of light across a photosensitive recording medium in a line (fast-scanning direction). While the beams sweep across the photosensitive recording medium, it is advanced in an orthogonal or "process" direction, commonly referred to as the slow-scan direction, such that the beams scan the recording medium in accordance with a raster scanning pattern. Printing is performed by serially modulating the intensity of each of the beams in accordance with a binary sample stream, whereby the recording medium is exposed to the image represented by the samples as it is being scanned.
Printers that sweep several beams simultaneously are referred to as multibeam or multispot printers. Moreover, dual or multispot lasers are considered to be an enabling technology for high speed printers operating at resolutions of about 600 spots per inch (spi) while producing output at greater than 80 pages per minute (ppm). Monolithic laser arrays, while providing the multispot capability, have typically been strongly sensitive to thermal droop and crosstalk when used in closely spaced lasers having interbeam spacings of less than 250 .mu.m.
The following disclosures, relating to both ROS printing devices and multibeam laser diodes, may be relevant:
U.S. Pat. No. 5,060,237 Patentee: Peterson Issued: Oct. 22, 1992 PA0 U.S. Pat. No. 4,892,371 Patentee: Yamada et al. Issued: Jan. 9, 1990 PA0 U.S. Pat. No. 4,884,857 Patentee: Prakash et al. Issued: Dec. 5, 1989 PA0 U.S. Pat. No. 4,796,964 Patentee: Connell et al. Issued: Jan. 10, 1989 PA0 U.S. Pat. No. 4,474,422 Patentee: Kitamura Issued: Oct. 2, 1984 PA0 U.S. Pat. No. 4,445,126 Patentee: Tsukada Issued: Apr. 24, 1984 PA0 U.S. Pat. No. 4,420,761 Patentee: Kitamura Issued: Dec. 13, 1983 PA0 U.S. Pat. No. 4,404,571 Patentee: Kitamura Issued: Sep. 13, 1983 PA0 U.S. Pat. No. 4,393,387 Patentee: Kitamura Issued: Jul. 12, 1983 PA0 U.S. Pat. No. 4,293,826 Patentee: Scifres et al. Issued: Oct. 6, 1981
The relevant portions of the foregoing disclosures may be briefly summarized as follows:
U.S. Pat. No. 5,060,237 discloses a laser diode array including a plurality of laser diode bodies affixed to a surface of a substrate. Each of the laser bodies includes a semiconductor junction therein which is capable of generating light in response to a voltage potential. An end surface of the body is angled at a forty-five degree angle so as to reflect the light generated by the diode in a direction which is orthogonal to the surface of the substrate.
U.S. Pat. No. 4,892,371 describes a semiconductor laser array light source and scanner wherein the laser light source emits one or more pairs of light beams. The light beams are collimated by a collimating lens and are subsequently directed along separate paths. Additional optical means are used to transmit or reflect certain of the light beams to one or more incident surfaces of the optical means so as to align the beams by controlling the angle of incidence and beam separation at a photosensitive surface.
U.S. Pat. No. 4,884,857 teaches a multiple spot printer which employs a laser system having multiple semiconductor lasers, an aperture plate, and an optical system as shown in FIGS. 4 and 5. Control of the spot locations at the surface of the photoconductor is achieved in two planes, first, using an aperture plate in the process plane, and second, using a single aperture plate in the scan plane.
U.S. Pat. No. 4,796,964 describes a method for using a multiple emitter solid state semiconductor laser in a raster output scanner. The overlapping beams are sequenced in ON/OFF operation to avoid any interbeam interference in a manner that assures that only one laser beam will be on at any given time. Hence, nonuniformity caused by optical interference of overlapping beams is prevented without the need for further modification of the optical properties of the beams (e.g., polarization and wavelength).
U.S. Pat. No. 4,474,422 discloses an optical scanning apparatus having a light source consisting of an array of aligned light sources. The beams from the light sources are collimated and deflected to sweep across a single photoreceptor. The beams are also displaced from each other in the cross-scan direction so that multiple lines can be scanned simultaneously across the photoreceptor. An object of U.S. Pat. No. 4,474,422 is to reduce variations in pitch by closely spacing individual lasers within the laser array in a compact structure.
U.S. Pat. No. 4,445,126 teaches an image forming apparatus which uses a plural beam source to scan a recording medium. The apparatus further includes an optical system for reducing the distance between the plural light beams at the surface of the recording medium. As illustrated (FIG. 4), a mirror having plural faces, angled so as to direct the outermost beams toward the imaging location, is used to increase the recording density on the surface of the recording medium.
U.S. Pat. No. 4,420,761 discloses a recording apparatus having plural dots arranged inclined to the scanning direction in order to increase the dot or scanning density. The phase difference caused by such inclination of a semiconductor laser array is compensated for using delay circuitry to generate a delay in the driving signals for the plural laser beams in accordance with the offset caused by the inclination.
U.S. Pat. No. 4,404,571 describes a multibeam recording apparatus comprising a scanner for scanning a recording medium with a plurality of light beams and a beam detector. The scanner employs a laser array light source having a plural number of semiconductor lasers arranged in a row. The beam detector utilizes a screen plate with a detection aperture which is smaller than the inter-beam spacing to individually detect each of the plural beams.
U.S. Pat. No. 4,393,387 teaches a beam recording apparatus including a semiconductor array laser light source having a plurality of light beam emitting points, a condensing optical system, an image rotator, and a rotatable polygon mirror for deflecting the light beams to the surface of a photosensitive drum. High density recording is enabled by controlling the angle of incidence, and therefore the interbeam spacing, of the outermost beams at the surface of the photosensitive drum.
U.S. Pat. No. 4,293,826 discloses a semiconductor injection laser having an optical feedback control incorporated within the same semiconductor chip. Stabilization of the of the laser output is accomplished by monitoring a portion of the light output with an optical detector, which then drives a feedback circuit to control the laser current. The patent further describes a hybrid semiconductor laser/detector arrangement which implements an array of laser/detector pairs on a single semiconductor substrate.
The relevant portions of the above-cited references are hereby incorporated by reference for their teachings.
In accordance with the present invention, there is provided a multispot laser, comprising a pair of laser diodes, means for supporting said laser diodes on opposed sides thereof, said supporting means conducting thermal energy generated during the operation of said laser diodes away from said laser diodes, and means, coupled to said supporting means, for dissipating the thermal energy.
In accordance with another aspect of the present invention, there is provided a printing machine having a photoreceptor which is exposed by a raster output scanning arrangement. The scanning arrangement comprises: a multispot laser, including first and second laser diodes for producing first and second beams, respectively; means for supporting said first and second laser diodes on opposed sides thereof, said supporting means conducting thermal energy generated during the operation of said laser diodes away from said laser diodes; and means, coupled to said supporting means, for dissipating the thermal energy. The raster output scanning arrangement further includes means for deflecting the first and second beams into an optical path, and means for directing the first and second beams toward a surface of the photoreceptor.